The present invention relates to monitoring of radio channel quality in wireless networks. More particularly, and not by way of limitation, the present invention is directed to a method and apparatus to support variable Channel Quality Information (CQI) reporting period in uplink transmissions in cellular wireless networks.
With ever-increasing demand for wireless communication and broadband services, there is an ongoing evolution of Third Generation (3G) and Fourth Generation (4G) cellular networks such as High Speed Packet Access (HSPA), Evolution-Data Optimized (EV-DO), Long Term Evolution (LTE), Worldwide Interoperability for Microwave Access (WiMAX), and the like to support ever-increasing performance with regard to capacity, peak bit rates, and coverage. Operators deploying these networks are continuously facing the need to more accurately “predict” the quality of the radio channel between two transceivers operating in their networks. A mobile communication environment such as the Third Generation Partnership Project's (3GPP) LTE network, the Evolved Universal Terrestrial Radio Access (EUTRA), or the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) air interface for LTE may require a base station to allocate resource blocks to a User Equipment (UE) where the resource blocks are generated by dividing the system bandwidth in the frequency domain. In such a mobile communication environment, the UE has to periodically feed back the Channel Quality Information (CQI) with respect to each frequency band via uplink signaling to the base station so as to enable the base station to more accurately “predict” channel quality for further downlink transmissions. The CQI feedback from the UE may indicate a combination of modulation scheme and channel coding rate that the base station should use to ensure that the block error probability experienced at the UE will not exceed ten percent.
In a wireless communication system employing Adaptive Modulation and Coding (AMC) in the downlink (for example, the LTE), CQI from the UEs is needed at the base station (e.g., an evolved Node-B (eNodeB or eNB)) to more accurately schedule the users for downlink transmissions, as mentioned above. Configuring the CQI reporting period is a complex problem because what is considered to be an “adequate” amount of information in the frequency direction and in the time direction in the CQI report may vary depending on the channel status and the moving speed of the UE. If the reporting period is very small, the quality of the CQI received from the UE is very good because of frequent delivery of CQI reports to the base station. In that case, the base station can more accurately keep track of the channel condition. However, a drawback of such frequent reporting is that it requires higher signaling from the UE, thereby reducing uplink throughput or capacity because more uplink frequency resources will be taken up for CQI reporting as opposed to carrying other user data. On the other hand, if the reporting period is fixed to a high value, then downlink throughput may be reduced dramatically for some channels due to the outdated CQI because reporting interval may be so long between two successive CQI's that channel quality information in one or more of such CQI's may become outdated by the time they are received at the base station, thereby requiring more retransmissions from the base station and, hence, reduced downlink throughput.
It is a common practice to set the CQI reporting interval to a fixed value. For example, in LTE, this value is set to either 5 ms or 10 ms depending on an operator's network implementation, even though there is no fixed rule in the current 3GPP standard regarding setting up of this value. Fixing the reporting period to a particular value for all the radio channels does not use the benefits of AMC in LTE, which allows variable or adaptive selection of coding bit rate (for Quadrature Phase Shift Keying (QPSK) modulation) depending on channel condition. In other words, the benefit of AMC (i.e., higher throughput through variable selection of coding bit rate) can still be achieved without rigidly fixing the CQI reporting interval to a single value, as is currently done in LTE network implementations.